Note: You know how I said I had a lot of desert research thanks to A Sign in Blood? Yeah. I so wasn't lying. Plus, I found more in another notebook. :-D This series has gotten longer, but I'm not going to post it all in one go (or series of goes). This second post will be the last one on deserts for a little while, so that I can post on a couple of other topics (agriculture, agrarian cultures vs. non-agrarian cultures, and siege engines). However, I will be coming back to it fairly soon. Desert posts after this one will include desert landforms, plants and species, desert cultures, and some more generalized worldbuilding thoughts.
Also, all temperatures in this post are given in Fahrenheit.
Part 1 | Part 2
Many (but not all!) deserts are hot. One reason for this is the fact that many form near the equator, where sunlight is more direct and temperatures higher. However, this is also exacerbated by another influence; dry ground, rock, and sand are less capable of absorbing heat than is wet ground, plants or water by itself. So, as these surfaces are heated by the sun (especially the very direct sunlight near the equator), they release their heat into the air which then becomes hotter, especially the first 6 or 7 feet of air closest to the ground. Above that, temperatures can be dramatically cooler.
Deserts can also get very cold, very quickly, having a large shift in temperature between day and night. The reason is that these surfaces (sand, stone, dry ground) release heat easily, so once the sun goes down and the heat is no longer being constantly replenished, the heat bleeds off and the air cools. This cooling and reheating of desert air perpetuates the dryness of the desert. Because sand is such a poor conductor of heat, the sand below the surface also takes a good while to warm up. This cooler area allows organisms and creatures to be somewhat protected from the heat.
Because it is the direct sunlight which heats up the hot deserts, areas protected from the sun and dry winds (as by rock formations, oases, etc.) can also form microclimates. The microclimates (which includes the below surface sand) can be cooler and—protected from the drying wind—sometimes more moist. It is in these areas which life is most likely to be found.
However, not all deserts form within 30 degrees of the equator. The deserts of Central Asia (Gobi, Takla-Makan, etc.), for instance are caused by continentality (the drying of the air as it moves inland, bleeding off its rain in the more coastal regions), the rainshadow effect (or a combination thereof), so while they are dry, they are not necessarily hot.
The Gobi, considered a cold desert, actually does have some very hot temperatures in summer (up to 122 degrees), but can also reach lows of -40 degrees. The average temperature there is around 37 degrees, but it can change very quickly, with shifts of up to 60 degrees happening in as little as 24 hours. Snowcapped or frosty dunes are a somewhat familiar sight in some regions of the Gobi. Like most non-equatorial climates, the temperature depends upon the season. In summer, temperatures get to about an average of 66 degrees, while an average late winter day might be around 2 degrees.
Still, this is just one particular desert, in order to give you an idea of what kinds of temperatures you could be looking at when building such a place. Polar deserts are, obviously, much colder for much longer periods, but also are a very different biome.
However, if your characters or culture live in, or must travel through, a place like the Gobi desert, they're going to have to be prepared for the massive shifts in temperature. They may not just have to deal with the cold, but also with extreme heat. Or the possibility of very cold nights, with almost pleasant days. Dealing with the challenges presented by our environments is one of the things which makes a culture, one of the things that defines it. Finding unique or interesting solutions to your culture challenges can really make them come alive.
And, lastly, a few more things to take into account when you're creating your deserts: continental drift, atmospheric changes, and volcanic activity. In short, things change and deserts were always something else at one point in time.
This is important to remember because your characters can, in fact, stumble upon lost civilizations chased away by volcanic eruptions, petrified forests half-buried beneath the sand, and fossilized creatures (practically, this mean hippos and elephants and such, but in fantasy or science fiction terms, dragons, dinosaurs, etc. Maybe even a dormant virus just waiting to be revived in an unsuspecting populace. You know, fun stuff! :-D).
So, keep in mind that things change over time and what is now a barely crossable obstacle for your characters or a challenging environment in which to build a civilization, could have once been a lush and thriving forest, a vast and powerful trade city that controlled most of the known world, or a massive tar pit in which many young dragons once met their tragic ends.
Even if you're not going to use those as plot elements, they make great visuals!
Next week, I'll be discussing basic agriculture and hopefully I'll be able to fit it in one post of a reasonable length! Well, we'll see… :-D